1. Field of the Invention
The present invention generally relates to detecting air leaks in a fuel measuring system and, more particularly, to determining the pneumatic health of a bubble-type fuel measuring system used in locomotives.
2. Description of the Prior Art
The invention is directed to an improvement for a bubble-type fuel measuring system such as that disclosed in U.S. Pat. No. 4,840,056 to Fernandez et al. which is herein incorporated by reference. The Fernandez et al. system, marketed under the name FUELLINK, is a bubble-type fuel measuring system which gauges fuel by measuring the pressure exerted by the fuel in a bubble tube positioned near the bottom of a fuel tank. The system employs one or more bubbling tubes located at predetermined locations in the tank and positioned at a fixed height from the tank bottom. A predetermined volume flow of air is forced through the tubes. Temperature sensors and pressure transducers periodically measure the temperature of the fuel and the air pressure supplied to the bubbling tubes, respectively. A microprocessor is used to convert temperature and pressure data to first determine the average normalized pressure that the fuel exerts at the bottom of the tank, and then from that, determine the level of fuel remaining in the tank.
Since the volume of air bubbled into the tank is a constant volume, the pressure required to bubble a given volume will be greater the fuller the tank. As fuel is consumed and the fuel level falls, more empty space becomes available in the tank thus reducing the pressure required to bubble the same volume of air into the tank. As can be readily ascertained, the accuracy of such a bubble-type fuel measuring system depends in large part on the pneumatic health of the system. If there are any air leaks in the system whatsoever, the pressure sensed at the bubble tube will be influenced by atmospheric back-pressure thereby making measured fuel readings inaccurate.